GB2317741A

GB2317741A - Magnetron cathode

Info

Publication number: GB2317741A
Application number: GB9726403A
Authority: GB
Inventors: Jong-Soo Lee
Original assignee: LG Electronics Inc
Current assignee: LG Electronics Inc
Priority date: 1995-12-12
Filing date: 1996-12-12
Publication date: 1998-04-01
Anticipated expiration: 2016-12-12
Also published as: GB9726403D0; GB2317741B

Abstract

An improved magnetron includes a center lead 211, an upper end shield 216 engaged to an upper portion of the center lead for preventing thermal electrons from escaping, a first cathode 223 fixed to an outer edge portion of the upper end shield, a cylindrical second cathode 214, and a lower end shield 212 engaged to the lower portion of the second cathode. In use, electrons emitted by the first cathode 223 strike the second cathode 214 and cause secondary emission.

Description

MAGNETRON The present invention relates to a magnetron, and in particular to an improved magnetron which is capable of elongating the life span of the magnetron, reducing the fabrication cost, and enhancing the performance of the system without using a filament in the conventional art.

This application is divided from UK Patent Application No 9625822.3 which discloses a magnetron, comprising a center lead, an upper end shield engaged to a portion of the center lead for preventing thermal electrons from escaping, a support wall surrounding the center lead, plate type first cathode fixed to the support wall, cylindrical secondary cathode surrounding the support wall, said secondary cathode having an elongated slit formed in an outer circumferential surface thereof, whereby a portion of the plate type first cathode extends outwardly through said slit and beyond the outer circumferential surface of the cylindrical secondary cathode, and a lower end shield engaged to a portion of the secondary cathode, whereby a small amount of electrons is radiated from the first cathode when a voltage is supplied to the first cathode, and the electrons collide with the outer wall of the cylindrical secondary cathode thus radiating a large amount of electrons from the outer wall of the cylindrical secondary cathode.

Figure 1A is a cross-sectional view illustrating a conventional magnetron, and Figure 1B is a cross-sectional view illustrating a cathode, vanes, and an anode of a conventional magnetron.

As shown therein, a cathode 3 is arranged in the center portion of a yoke 30 encapsulating inner components of the magnetron.

A cylindrical anode 1 is arranged in the outer portion of the cathode 3, and a plurality of spaced-apart vanes 2 are radially arranged in the anode 1, each outer end of which vanes 2 is fixed to the inner circumferential surface of the anode 1.

In addition, an inner strap ring 9 is arranged on the vanes 2, and an outer strap ring 9 having a greater diameter than that of the inner strap 9 is arranged in the outer side of the inner strap 9.

Here, since the inner strap ring 9 and the outer strap ring 10 are alternately and fixedly engaged to the vanes 2, namely, the vanes 2 to which the inner strap ring 9 is fixedly engaged is not engaged to the outer strap ring 10. Here, the neighboring vanes 2 have a phase difference of 1800 from one another and are electrically connected to one another.

The construction of the cathode 3 will now be explained in more detail. As shown in Figure 1B, an upper end shield 7 for supporting a filament 5 is arranged on the top portion of the filament 5 which is spirally formed so as to effectively radiating electrons.

A rim portion 6 having a larger diameter than the outer diameter of the filament 5 is formed in the upper end shield 7 so as to prevent thermal electrons generated from the filament 5 from escaping to the outside of an operational space 4.

A lower end shield 8 is arranged in a lower portion of the filament 5 so as to upwardly support the lower portion of the filament 5.

Permanent magnets 12 are arranged in upper and lower portions of the anode 1 as shown in Figure 1A.

In addition, a vacuum resonant portion 14 is formed in a portion surrounded by two neighboring vanes 2 and the anode 1, one side of which vacuum resonant portion 14 is open toward the cathode 3, and the resonating frequency of the magnetron is determined in accordance with the resonant frequency.

The operation of the conventional magnetron will now be explained with reference to Figures 1A through 1C.

First, a voltage is supplied to the cathode 3, an electric field is generated between the cathode 3 and the vanes 2 in the operational space 4, and an electric magnetic field is generated in the direction parallel to a center stem Sa of the cathode 3.

Therefore, a high frequency electric field is generated in the vacuum resonant portion 14 and is focused to an end portion of each vane 2, and a part of the high frequency electric field is leaked into the interior of the operational space 4.

In addition, since the inner strap ring 9 and the outer strap ring 10 are alternately engaged to the vanes 2, an electric potential is rapidly changed between the vanes 2, and the electrons radiated from the cathode 3 circles in the operational space 4 and interacts with the high frequency electric field therein, for thus oscillating microwaves.

In addition, the thusly oscillated microwaves are transferred to the outside of the magnetron through an antenna 11 connected to the vanes 2. Here, since a part of electrons is changed into heat energy, cooling fins 13 are arranged in the outer portion of the anode 1 so as to prevent the temperature from being increased due to the heat applied thereto.

A filter box 20 having a chalk coil 21 and a through type condenser 22 is arranged below the yoke 30 for preventing the leakage of a unnecessary radiating wave which causes an interference with respect to a communication system such as a television, a radio, etc when an electric wave having a range of 2450MHz including a range from hundreds of KHz to tens of GHz is generated when a voltage is applied to the system.

The conventional magnetron which uses the filament has the following disadvantages.

First, since a current is applied to heat the filament, a filament voltage supply system is additionally necessary, and since the filament becomes activated at a temperature of about 1700 , a center lead, a side lead, and other elements which support the filament should be made of an expensive molybdenum having a high melting point.

Second, since the voltage of about 30W through SOW is consumed so as to heat the filament, the efficiency of the magnetron is degraded.

Third, since the heat source of about 17000C is transferred to the chalk coil through the center lead, the side lead, etc, it is impossible to thermally control the chalk coil.

Fourth, it is impossible to effectively cool the magnetron because the resonant space in which the cylindrical anode body and vanes are arranged is heated therein due to the heat from the cathode having a temperature of about 17000C.

Fifth, since the strength of the filament is very weak, it may be easily broken by external impact, so that the life span of the magnetron is shortened.

Sixth, since the filament is operated after a lapse of a predetermined time after a voltage is supplied to the filament, electric wave noise occurs during the abnormal operation, for thus degrading the performance of the magnet.

Accordingly, it is an aim of certain embodiments of the present invention to provide a magnetron which overcomes the problems encountered in the conventional art.

It is a further aim of certain embodiments of the present invention to provide an improved magnetron which is capable of elongating the life span of the magnetron, reducing the fabrication cost, and enhancing the performance of the system without using a filament in the conventional art.

To achieve the above aims, in accordance with a first embodiment of the present invention, there is provided a magnetron, which includes a center lead, an upper end shield engaged to an upper portion of the center lead for preventing thermal electrons from being escaped, a plate type first cathode arranged below the upper end shield and fixed to one side of the support wall surrounding the center lead, a cylindrical secondary cathode having an elongating slit formed in an outer circumferential surface thereof, through which slit a part of the plate type first cathode is outwardly extended beyond the outer circumferential surface of the cylindrical secondary cathode, and a lower end shield engaged to the lower portion of the secondary cathode, whereby a small amount of electrons is radiated from the first cathode when a voltage is supplied to the first cathode, and the electrons collide with the outer wall of the cylindrical secondary cathode through the slit, for thus radiating a large amount of electron inn cooperation with the collision energy between the electrons and the outer wall of the cylindrical secondary cathode.

To achieve the above aims, in accordance with a second embodiment of the present invention, there is provided a magnetron, which includes a center lead, an upper end shield engaged to an upper portion of the center lead for preventing thermal electrons from being escaped, a first cathode fixed to an outer edge portion of the upper end shield, a cylindrical second cathode arranged within the first cathode, and a lower end shield engaged to the lower portion of the secondary cathode.

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative o= the present invention, and wherein: Figure 1A is a cross-sectional view illustrating a conventional magnetron; Figure 1B is a cross-sectional view illustrating a cathode, vanes, and an anode of a conventional magnetron; Figure 1C is a horizontal cross-sectional view illustrating the cathode, the vanes, and the anode of Figure 1; Figure 2A is a vertical cross-sectional view illustrating the construction of a cathode of a magnetron according to a first embodiment of the present invention; Figure 2B is a horizontal cross-sectional view illustrating the construction of the cathode of Figure 2A embodying the present invention; Figure 3A is a vertical cross-sectional view illustrating the construction of a cathode of a magnetron according to a second embodiment of the present invention; Figure 3B is a horizontal cross-sectional view illustrating the construction of the cathode of Figure 3A embodying the present invention; Figure 4 is a horizontal cross-sectional view illustrating the construction of cathode of a magnetron according to a third embodiment of the present invention; Figure 5A is a cross-sectional view illustrating a secondary cathode of a magnetron embodying the present invention so as to explain an ion activation state; and Figure 53 is a cross-sectional view illustrating the secondary cathode of Figure 5A when the secondary cathode is heated by an activation device up to a predetermined temperature so as to explain the rearrangement of ions.

The magnetron according to a first embodiment of the present invention will now be explained with reference to Figures 2A and 2B.

As shown therein, a cathode of the magnetron according to the first embodiment of the present invention includes a vertical plate type field emission cathode (FEC) (a first cathode) 113, and a hollow secondary emission body (SEB) (a second cathode) 114.

The first cathode 113 arranged below an upper end shield 116 for preventing the leakage of a thermal electron is fixed to a portion of a support wall 117 surrounding a cylindrical center lead 111.

Here, one lengthy side of the first cathode 113, as shown in Figure 2B, is fixedly inserted into a portion of the support wall 117, with another lengthy side of the first cathode 113 being extended through an elongated slit ISO formed in the outer circumferential surface of the second cathode 114.

If a voltage is supplied to the first cathode 113, a small amount of electrons is radiated from the first cathode 113.

In addition, the cylindrical second cathode 114 surrounds the support wall 117.

Namely, the cylindrical second cathode 114, the support wall 117, and the slit 150 have a predetermined shaped construction therebetween so that when a small amount of electrons is radiated from the first cathode 113 and is circled near the slit 150, and the electrons collide with the outer wall of the second cathode 114, whereby a large amount of electrons can be obtained in cooperation with a collision energy which occurs during the collision between the electrons and the outer wall of the second cathode 114.

As shown in Figure 2A, a secondary cathode activation apparatus 115 for activating the second cathode 114 is arranged between the first cathode 113 and the second cathode 114, with both ends of the secondary cathode activation apparatus 115 contacting with the first cathode 113 and the second cathode 114.

The support wall 117 is made of either Ni or Zr which has a high strength. Here, the secondary cathode activation apparatus 115 is used for supplying a voltage to the second cathode 114. After the activation of the second cathode 114, the secondary cathode activation apparatus 115 is removed.

In the drawings, reference numeral i12 denotes a lower end shield.

Figure 3A is a vertical cross-sectional view illustrating the construction of a cathode of a magnetron according to a second embodiment of the present invention, and Figure 3B is a horizontal cross-sectional view illustrating the construction of the cathode of Figure 3A according to the present invention.

As shown therein, a donut-shaped first cathode 223 is fixed to an outer lower edge portion of an upper end shield 216, and a lengthy cylindrical secondary field emission cathode 214 is fixed to one side of a secondary cathode activation apparatus 215 contacting with the outer circumferential surface of the upper end shield 216.

Here, the inner surface of the donut shape first cathode 223 contacts with the outer surface of the cylindrical secondary cathode 214.

In the drawings, reference numeral 211 denotes a center lead, and 212 denotes a lower end shield.

In the magnetron according to the third embodiment of the present invention, as shown in Figure 4, identically with the second embodiment, the first cathode is fixed to an outer edge portion of the upper end shield 316. However, the donut type first cathode 223 is divided into a predetermined number in its lengthy direction thereof, and a vertical plate type field emission cathodes is inserted into each slit formed between neighboring first cathodes 324, with each side of the vertical plate type field emission cathodes being fixed to the outer circumferential surface of a cylindrical secondary field emission cathode 314 surrounding a center lead 311.

In both the second and third embodiments of the present invention, a secondary cathode activation apparatus 315 is arranged between the inner surface of an end shield 316 and the cylindrical secondary cathode 314. Identically to the first embodiment of the present invention, the secondary cathode activation apparatus 315, which is basically used so as to supply a predetermined voltage to the secondary cathode, is removed after the fabrication of the magnetron.

Therefore, identically to the second and third embodiments of the present invention, when a predetermined voltage is supplied to the first cathode, a small amount of electrons is radiated therefrom. The electrons radiated from the first cathode circles and collides with the outer wall of the secondary cathode, for thus radiating a large amount of electrons in cooperation with a collision energy between the electrons and the outer wall of the secondary cathode.

In addition, the material of the first cathode satisfies the following conditions.

First, the first cathodes 113, 223, and 324 are made of a material having a lower work function, which is capable of radiating electrons even when a lower voltage is supplied thereto ( < 3eV).

In more detail, generally, it is known that oxygen combination serves to increase the work function of the material. As a chemical combination of oxygen, there are a passivation and an oxidation in a metallic and semiconductor field at lower temperature.

Here, the porosity coefficient a is obtained through the following equation.

a = n(Vok / Vop) -------------- (1) where Vok denotes a molecular size of oxygen, Vop denotes a nuclear size, and n denotes a ratio between the number of atoms of a metal and the number of all atoms of oxygen molecular.

When the porosity coefficient a is less than 1, a poros layer is formed during an oxidation, through poros layer oxygen can easily penetrate into the metal.

When the porosity coefficient a is greater than 1, an intensive layer of the oxide material is formed during the oxidation, so that the penetration of the oxygen into the metal is not performed.

Second, since the thermal characteristic of a material of the first cathodes 113, 223, and 324 is determined by the temperature characteristic of the first cathodes 113, 223, and 324, the strength, an electrical conductivity, and a thermal conductivity must be high.

The materials which satisfies the above-described conditions are Ta, Nb, Si, Al, etc.

In addition, the second cathodes 114, 214, and 314, as shown in Figures SA and 5B, include a base layer 101 and an outer layer 102, and the base layer 101 is formed of one selected from the group comprising Ni and Zr, and the outer layer 102 is formed of one selected from the alloy group comprising an alloy of Ba and Al, an alloy of Pd and Ba, and an alloy of Re and La.

On the assumption that the alloy of Ba and Al is used, at the initial stage, Ba and Al are mixed with each other. When heating the outer layer 102 by applying a predetermined voltage thereto by using the secondary cathode activation apparatuses 115 and 215 up to 4000C - 6000C, as shown in Figure 5B, Ba gathers at an edge portion of the outer layer, for thus activating the outer layer, whereby it is possible to increase the electron radiation effect.

As described above, the magnetron according to the present invention does not use the filament which was used in the conventional art as a key element. Namely, when a predetermined voltage is supplied to the first cathode, the first cathode radiates a small amount of electrons, and the electrons collide with the outer wall of the secondary cathode, for thus radiating a large amount of electrons. In other words, the magnetron according to the present invention provides a double structure of first and second cathodes, for thus removing the filament compared to the conventional art, whereby it is possible to elongate the life span of the product, reduce the fabrication cost, and improve the performance of the product.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as recited in the accompanying claims.

Claims

CLAIMS:

1. A magnetron comprising: a center lead; an upper end shield engaged to an upper portion of the center lead for preventing thermal electrons from being escaped; a first cathode fixed to an outer edge portion of the upper end shield; a cylindrical second cathode arranged within the first cathode; and a lower end shield engaged to the lower portion of the secondary cathode.

2. The magnetron of claim 1, further comprising a secondary cathode activation apparatus arranged between the inner surface of the upper end shield and the secondary cathode, with both ends of the secondary cathode activation apparatus contacting with the inner surface of the upper end shield and the secondary cathode.

3. The magnetron of claims 1 or 2, wherein said first cathode is ring-shaped.

4. The magnetron of any of claims 1, 2 or 3, wherein said first cathode has a plurality of spaced-apart slits formed on the circumferential surface of the first cathode, through which each slit a plate type first cathode is outwardly extended from the outer circumferential surface of the cylindrical second cathode.

5. The magnetron of any of claims 1 to 4, wherein the inner circumferential surface of the first cathode and the outer circumferential surface of the cylindrical second cathode are spaced apart from each other by a predetermined distance.

6. The magnetron of any of claims 2 or 3 to 5 when dependent on claim 2, wherein said secondary cathode activation apparatus serves to provide a predetermined voltage to the cylindrical secondary cathode when the secondary cathode activation apparatus is first used, and then it is removed after the secondary cathode is activated.

7. The magnetron of any of claims 1 to 6, wherein said cylindrical secondary cathode includes a base layer and an outer layer.

8. The magnetron of any of claims 1 to 7, wherein said plate type first cathode is made of one selected from the group comprising Ta, Nb, Si, and Al.

9.. The magnetron of claim 7 or claim 8 when appended to claim 7, wherein said base layer is formed of one selected from the group comprising Ni and Zr.

10. The magnetron of claims 7 and 9 or 8 when dependent on claim 7, wherein said outer layer is formed of one alloy selected from the group comprising an alloy of Ba and Al, an alloy of Pd and Ba, and an alloy of Re and La.

11. The magnetron of any of claims 1 to 10, wherein said support wall is made of one selected from the group comprising Ni and Zr.

12. An improved magnetron substantially as hereinbefore described with reference to Figures 2A, 2B, SA and 5B, Figures 3A, 5A and 5B, or Figures 4, 5A and SB of the accompanying drawings.

13. A magnetron, comprising: a center lead; an upper end shield engaged to an upper portion of the center lead for preventing thermal electrons from being escaped; a plate type first cathode arranged below the upper end shield and fixed to one side of the support wall surrounding the center lead; a cylindrical secondary cathode having an elongating slit formed in an outer circumferential surface thereof, through which slit a part of the plate type first cathode is outwardly extended beyond the outer circumferential surface of the cylindrical secondary cathode; and a lower end shield engaged to the lower portion of the secondary cathode, whereby a small amount of electrons is radiated from the first cathode when a voltage is supplied to the first cathode, and the electrons collide with the outer wall of the cylindrical secondary cathode through the slot, for thus radiating a large amount of electron inn cooperation with the collision energy between the electrons and the outer wall of the cylindrical secondary cathode.

14. The magnetron of claim 13, further comprising a cylindrical secondary cathode activation apparatus arranged between the first cathode and the cylindrical secondary cathode, with both ends of the secondary cathode activation apparatus contacting with the first cathode and the secondary cathode.

15. The magnetron of claims 13 or 14, wherein said cylindrical secondary cathode includes a base layer and an outer layer.

16. The magnetron of claims 14 or 15 when dependent upon claim 14, wherein said secondary cathode activation apparatus is directed to providing a predetermined voltage to the cylindrical secondary cathode when the secondary cathode activation apparatus is first used, and after the secondary cathode is activated, the secondary cathode activation apparatus is removed.

17. The magnetron of any of claims 13 to 16, wherein said plate type first cathode is extended from the outer circumferential surface of the secondary cathode.

18. The magnetron of any of claims 13 to 17, wherein said plate type first cathode is extended up to a portion between the outer circumferential surface and the inner circumferential surface of the cylindrical secondary cathode.

19. The magnetron of any of claims 13 to 18, wherein said plate type first cathode is made of one selected from the group comprising Ta, Nb, Si, and Al.

20. The magnetron of claim 15 or any of claims 16 to 19 when appended to claim 15, wherein said base layer is made of one selected from the group comprising Ni and Zr.

21. The magnetron of any of claims 15 to 20, wherein said outer layer is made of one alloy selected from the group comprising an alloy of Ba and Al, an alloy of Pb and Ba, and an alloy of Re and La.